In an information processing system including an information processing apparatus, a communication processing apparatus, and a server, for example, an information processing apparatus such as a home personal computer (PC) or a home electrical appliance may be accessed through the server from an external apparatus such as a mobile telephone. The communication processing apparatus is a router having a network address translation (NAT) function or the like, for example.
The communication processing apparatus can executes address translation of a packet transmitted from the side of a local area network (LAN) of the communication processing apparatus can relay the packet to the side of a wide area network (WAN). On the other hand, address translation is not necessarily executed for all packets transmitted from the WAN side of the communication processing apparatus for relaying to the LAN side. Therefore, it is necessary to enable the communication processing apparatus to relay a packet transmitted from the server to the information processing apparatus.
As one method for enabling the communication processing apparatus to relay a packet transmitted from the server, a method of setting port mapping in the communication processing apparatus using universal plug and play (UPnP), etc., is available. The port mapping setting is setting to relay a packet transmitted from the WAN side (server side) to a predetermined port of the communication processing apparatus to a predetermined port of the information processing apparatus. The port mapping setting is made, whereby the packet transmitted from the server to the predetermined port of the communication processing apparatus is relayed to the predetermined port of the information processing apparatus.
As another method for enabling the communication processing apparatus to relay a packet transmitted from the server, a method of repeatedly transmitting the packet to the server from the information processing apparatus through the communication processing apparatus is available. This configuration is disclosed in International Patent Laid-Open No. WO2004/030292, for example. When a packet is transmitted from the LAN side to the WAN side, the communication processing apparatus having the NAT function such as a router converts the private Internet protocol (IP) address and port number on the LAN side are translated into the global IP address and port number on the WAN side.
When a packet from the WAN side is received, the packet is filtered according to a predetermined reception filter rule and inverse translation of address translation is executed, whereby the packet is passed to the information processing apparatus. The reception filter rule for determining the reception possibility of the packet from the WAN side relative to the port to which the packet is transmitted from the LAN side of NAT includes an Address Sensitive filter for receiving the packet only from the packet transmission address from the port, a Port Sensitive filter for receiving the packet only from the packet transmission port from the port, and a No filter meaning that no filter exists.
The time for executing such address translation is set in the communication processing apparatus. Specifically, address translation of a packet received from the WAN side is not executed after the expiration of a predetermined time period since the last address translation between the WAN side and the LAN side (new address translation is executed for a packet received from the LAN side). That is, the packet from the WAN side is not received at the information processing apparatus and the information processing apparatus cannot be accessed via the server from an external apparatus such as a mobile telephone. The predetermined time period will be called the port maintaining time.
Therefore, a packet is repeatedly transmitted to maintain the port of the communication processing apparatus (namely, to allow the packet from the WAN side to be transmitted via the communication processing apparatus to the information processing apparatus), whereby it is made possible to access the information processing apparatus via the server from an external apparatus such as a mobile telephone. Therefore, if port mapping is set in the communication processing apparatus using UPnP, etc., it is not necessary to repeatedly transmit a packet to the server.
However, port mapping cannot necessarily be set in all communication processing apparatus using UPnP, etc. Some communication processing apparatus are not compatible with the standard of UPnP, etc., and port mapping cannot be set in the communication processing apparatus. On the other hand, an increase in the traffic of communication lines of the Internet, etc., can result from enabling the information processing apparatus to receive the packet transmitted from the server by repeatedly transmitting a packet without setting port mapping relative to all communication processing apparatus.